The overall goal of our studies is to understand the regulation, function, and disease association of the keratin intermediate filament (IF) proteins, keratin polypeptides 8, 18 and 19 (K8, K18 and K19). These keratins are the major IF proteins in epithelia of digestive organs. The functions of keratins are becoming increasingly understood and their significance is highlighted by their growing association with a broad range of human diseases. For example, several skin diseases are caused by mutations in epidermal keratins, and K8 and K18 mutations predispose to liver disease and its progression. Our overall hypothesis is that IF proteins, one of the three major cytoskeletal protein families that include actin microfilaments and tubulin microtubules, play important physiologic and disease-related roles whose significance is rapidly unfolding. We propose to use two approaches: (a) a targeted approach to understand specific aspects of keratin regulation; namely glycosylation, keratin associated proteins (KAPs), and keratin cleavage by caspases, and (b) an unbiased approach to explore results from expression profiling analysis of wild-type and keratin-8 null mouse colonocytes to understand the consequent colitis and colonic hyperplasia that are due to keratin absence. Our specific aims are: (i) Study the functional significance of keratin glycosylation in digestive organs. The hypothesis for Aim#1 is that keratin glycosylation plays an important role in regulating the phosphorylation of other essential cellular proteins. (ii) Characterize the interaction and function of the association between keratins and non-muscle myosin. The hypothesis for Aim#2 is that KAPs regulate keratin function and that KAP function may be regulated by keratins. (iii) Examine the utility of assessing keratin apoptotic fragments in patients with acute liver failure. The hypothesis for Aim#3 is that apoptosis during acute liver injury results in leakage of the highly abundant keratin caspase-cleaved fragments into the circulation and that the presence of such fragments will have diagnostic and/or prognostic implications. (iv) Understand how keratins and luminal microbes modulate colonic hyperproliferation via apoptotic effects. The hypothesis for Aim#4 is that changes in colonocyte gene and cell surface expression in response to keratin absence, coupled with the presence of luminal bacteria, inhibit apoptosis. Our proposal includes cell biologic, molecular, cell culture, genetic models and human disease-related studies aimed at helping understand the regulation, function and disease aspects of keratins in digestive organs. Fundamental findings that we hope to show include a function for keratin glycosylation, myosin as a novel phosphorylation-dependent keratin binding partner, keratin apoptotic fragments as diagnostic or prognostic markers in liver disease, and an unexpected role of keratins in the colon as proapoptotic proteins as contrasted with their role in the liver as anti-apoptotic.